Debugger: error when debug code in "-gdb-set follow-fork-mode child" with popen

Bug type: Debugger

Describe the bug

• OS and Version: Debian 9.13
• VS Code Version: 1.60.0
• C/C++ Extension Version: v1.6.0
• Other extensions you installed (and if the issue persists after disabling them):
• A clear and concise description of what the bug is.

Try to debug forked process by using this command:

                {
                    "description": "The new process is debugged after a fork. The parent process runs unimpeded.",
                    "text": "-gdb-set follow-fork-mode child",
                    "ignoreFailures": true
                }

However, the program being debugged has popen() that creates several threads, which crashes the debug process.

I guess vscode might "set follow-fork-mode child" right before calling fork() and immediately unset it after fork().

To Reproduce
Please include a code sample and launch.json configuration.
Steps to reproduce the behavior:

1. Touch main.c
2. Write the code in the file:

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main()
{
    printf("start popen\n");
    popen("echo hello", "r");
    printf("start fork\n");

    int pid = fork();

    if (pid== 0)
        printf("Hello from Child!\n");
  
    // parent process because return value non-zero.
    else
        printf("Hello from Parent!\n");

    return 0;
}

3. Generate default launch.json and task.json
4. Modify launch.json as:

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "gcc-6 - Build and debug active file",
            "type": "cppdbg",
            "request": "launch",
            "program": "${fileDirname}/${fileBasenameNoExtension}",
            "args": [],
            "stopAtEntry": false,
            "cwd": "${fileDirname}",
            "environment": [],
            "externalConsole": false,
            "MIMode": "gdb",
            "setupCommands": [
                {
                    "description": "Enable pretty-printing for gdb",
                    "text": "-enable-pretty-printing",
                    "ignoreFailures": true
                },
                {
                    "description": "The new process is debugged after a fork. The parent process runs unimpeded.",
                    "text": "-gdb-set follow-fork-mode child",
                    "ignoreFailures": true
                }
            ],
            "preLaunchTask": "C/C++: gcc-6 build active file",
            "miDebuggerPath": "/usr/bin/gdb"
        }
    ]
}

4. Set some breakpoints from the start of main and debug step-by-step.
5. Keep next-ing until debug process dies unnaturally.

Additional context
If applicable, please include logging by adding "logging": { "engineLogging": true, "trace": true, "traceResponse": true } in your launch.json
Add any other context about the problem here including log or error messages in your Debug Console or Output windows.

Inizia con il riproduttore main.c e i setupCommands di launch.json usando -gdb-set follow-fork-mode child, quindi abilita engineLogging, trace e traceResponse. Analizza il comportamento del debugger intorno a popen(), fork() e al processo figlio; il lavoro è completato quando il debug del processo figlio non causa più la terminazione imprevista del processo di debug.